The present application describes a particular type of orbit, and constellations of multiple satellites in communication with the earth, employing this particular type orbit. More specifically, orbits are described which are capable of providing enhanced communications capacity or performance for a particular latitude band or bands at a particular local time or times of day at any selected geographical location.
Sun-synchronous satellite orbits are known. A basic sun-synchronous orbit is described in U. S. Pat. No. 5,582,367, having common inventorship. This sun-synchronous orbit describes an array of satellites in one or more elliptical orbits.
Mobile Communication Holdings, Inc., the assignee of the present application, has pioneered the concept of sun synchronous elliptical orbits. These orbits include certain advantages. Specifically, the sun-synchronous elliptical orbit avoids some of the problems associated with geosynchronous satellites, including their relatively high height requirement, associated time delay high payload, and other certain problems.
Elliptical orbits and elliptical orbit constellations are also known. The Russian Molniya series of orbits are in this category. They are primarily intended to provide augmented coverage to the Northern Hemisphere, and are constrained to an orbital inclination of approximately 63.4 degrees to maintain their apogees in the Northern Hemisphere. These orbits are not sun-synchronous and generally have an argument of perigee at or very close to xe2x88x9290 degrees.
In order to obtain sun-synchronicity while maintaining the apogee at a fixed latitude, satellites are constrained to lie in orbital planes very close to 116.6 degrees. To date, these orbits have had arguments of perigee at or close to xe2x88x9290 degrees, similar to the Molniya orbits, such that their apogees occur at latitudes in the vicinity of 63.4 degrees North. They provide excellent Northern Hemisphere earth coverage down to about 25 degrees North latitude.
Sun synchronous orbits of this type, however, may have effects based on their interaction with the Van Allen radiation belt.
The present invention teaches a sun-synchronous satellite orbit having a line of apsides lying in or near (i.e., within 0-60 degrees, more preferably within 0-15 degrees) of the equatorial plane. These elliptical orbits have apogees and perigees near the Equator, e.g., between 0 and 15 degrees inclination, more preferably 0-10 degrees inclination relative to the Equator. These orbits are based on the inventor""s recognition that locating the orbits in this way can avoid certain effects from the radiation belt.
Other aspects are described with reference to the claims and the specification that follows.